Wood products have been used as utility poles, railway ties and construction materials in a wide variety of industries. Without proper treatment, wood products deteriorate and are susceptible to weathering, insects (termites, carpenter ants, and beetles), marine borers (mollusks and crustaceans), bacteria and fungi (stains, white rot, soft rot, and brown rot). Wood treatment is required to prevent these problems.
Borates are a broad spectrum insecticide commonly used in the treatment of wood. They have the advantage of being readily diffusible into the interior of wood and exhibit low mammalian toxicity. However, borates have disadvantages in that they are susceptible to leaching and do not adequately protect against soft rot fungi. Exemplary borates include sodium octaborate, sodium tetraborate, sodium pentaborate, boric acid, disodium octaborate tetrahydrate, boron esters and PBA-phenylboronic acid.
Creosote is another chemical commonly used for the treatment of wood. It comprises over 300 different compounds, the majority of which are polycyclic aromatic hydrocarbons. Creosote is a broad spectrum biocide, and, unlike borates, is able to protect against soft rot fungi. However, creosote is unable to penetrate into the interior of heartwood.
A two stage “envelope” treatment process has been developed to address the problems associated with treatment by borates or creosote individually. The wood is first immersed in a borate solution and let set for about six weeks under cover, thereby allowing the borate to diffuse throughout the wood. This first step is followed by treatment with creosote to form a hydrophobic envelope around the wood. The creosote envelope prevents leaching of the borate and is active against soft rot fungi. As such, the envelope treatment is highly effective in reducing and/or preventing wood deterioration due to microorganisms.
However, the two step envelope treatment also suffers from serious drawbacks. First, it requires six week borate treatment to diffuse, which is extremely time consuming and inefficient. Additional time is required for the wood to dry of up to several additional weeks before creosote can be encapsulated.
Finally, extra handling and equipment is required to carry out the process. As such, new methods of applying the envelope treatment that require less time and handling and allow for the use of wood with a higher moisture content are urgently needed.